A single 18650 can do much more than 30W. My Emisar D4v2 can pull ~17A from a single 18650 on turbo mode, and it's not much bigger than the battery itself. I carry it on my belt everyday. It starts to get a little uncomfortable to hold and eventually triggers the thermal protection after about a minute of continuous turbo use, but that's more than enough for a quick prank. It runs an open source firmware too, so I could theoretically swap in some IR LEDs and program it with the appropriate modulation.